refactor purge to use foreign key cascade

nomen/settings.py

@@ -37,14 +37,8 @@ You may want to `{ctx.clean_prefix}nomen export` first"""
         to_purge = await confirm(ctx, msg)
 
         if to_purge:
-            await self.bot.db.execute(
-                """
-            DELETE FROM keywords WHERE user_id=?;
-            DELETE FROM users WHERE user_id=?;
-            DELETE FROM user_ignores WHERE user_id=?;
-            """,
-                (ctx.author.id,),
-            )
+            # Foreign key constraints will automatically cascade to delete dependent data
+            await self.bot.db.execute("DELETE FROM users WHERE user_id=?", (ctx.author.id,))
             await self.bot.db.commit()
             await ctx.send("Deleted all user data.")
         else: